/Engine/Source/Runtime/Slate/Public/Widgets/Views/STreeView.h
Set the RootItemsSource. The tree will generate widgets to represent these items.
void SetRootItemsSource ( [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [UE::Slate::Containers::TObservableArray](API\Runtime\SlateCore\Containers\TObservableArray)< ItemType >> InItemsSource )